1. Field of the Invention
the present invention relates to a scanning arrangement and method for determining the shape, size or other three-dimensional surface characteristics of an object, such as colour for example.
2. Description of the Related Art
A number of patents and published patent applications disclose optical scanning systems which rely on a scanned laser beam or the like for determining the shape of an object. Usually such systems utilise a fixed mounting for the scanning system and utilise optical triangulation for determining depth information. Examples of such systems include U.S. Pat. No. 4,627,734 (Rex), EP-B-233,920 (Addleman) and WO 94/15173 (Crampton).
There is a need for a scanner for determining shape or other surface characteristics which can be hand-held. As far as we are aware, only one such system is known, namely that disclosed in U.S. Pat. No. 5,198,877 (Schulz) and its equivalent EP-A-553,266.
The Schulz system requires an externally generated coordinate system defined by an array of photodetectors which detects an array of pilot lights on the scanner. Hence the scanner can only be used within this coordinate system and furthermore the array of pilot lights must be kept in view by the array of photodetectors, which further restricts the mobility of the scanner. This is a serious disadvantage because it is normally necessary to scan the object of interest from all sides in order to build up a complete picture of its surface.
An object of the present invention is to provide a scanning arrangement and method in which the scanner can be moved freely without reference to the position of its mounting.
Accordingly the invention provides a scanning arrangement for determining the shape or other three-dimensional surface characteristics of an object, the arrangement comprising a scanning device which is freely movable relative to said object, the device comprising:
a) an optical projector for projecting a predetermined pattern onto a region of the surface of the object, and PA1 b) an optical detector for detecting the coordinates or other surface characteristics of said region and for generating output signals representative of such coordinates or other surface characteristics, PA1 c) processing means coupled to said detector for generating a set of output data representing said surface characteristics of a scanned portion of the surface of said object, PA1 d) combining means coupled to said processing means for combining sets of such output data derived from overlapping scans of said surface into a common set of output data by appropriate rotations and translations, said combining means optionally including further processing means for calculating said rotations and translations from subsets of respective sets of such output data which relate to a common area of said surface, PA1 e) optionally, inertial sensing means for detecting movement of said scanning device relative to said object and generating output signals representative of such movement, and PA1 f) correcting means for correcting for movement of said scanning device relative to said object between successive scans, PA1 i) output signals from said inertial sensing means (if present) PA1 ii) output data from said further processing means (if present), PA1 i) projecting from the scanning device a predetermined optical pattern onto a region of the surface of the object, PA1 ii) optically detecting the coordinates or other surface characteristics of said region with an optical detector mounted on said scanning device, PA1 iii) deriving a set of output data representing said coordinates or other surface characteristics of said region, PA1 iv) repeatedly scanning said optical pattern over said object in overlapping fashion and deriving further sets of output data from overlapping scans, and PA1 v) correcting said sets of output data for movement of said scanning device relative to said object between successive scans either by sensing movement of said scanning device relative to said object with an inertial sensing means (50, 51) or by determining the rotations and/or translations needed to superimpose subsets of respective sets of said output data which relate to an area of said surface which is common to said sets.
the arrangement further including:
said correcting means being responsive to at least one of:
the arrangement including either said inertial sensing means or said further processing means or both.
In one embodiment the scanning device carries inertial sensing means for sensing its linear acceleration and rotation sensing means for sensing its rate of rotation. By double integrating the output of the inertial sensing means with respect to time and integrating the output of the rotational sensing means with respect to time the position and attitude of the scanning device can be detected throughout the scanning process and these parameters can be applied by the correcting means to correct the output of the optical detector.
In another embodiment the correcting means effectively consists of the combining means, which in this embodiment comprises further processing means for determining the translations and/or rotations required to combine the data from successive scans.
The invention also provides a method of determining the shape or other three-dimensional surface characteristics of an object by means of a scanning device which is freely movable with respect to the object, the method comprising: